What are the different types of C purlins

C purlins, the unsung heroes of many roofs, play a vital role in supporting the weight and structure of roofing sheets and other building elements. 

This blog dives into the world of C purlins, exploring their different types, standard sizes, and the advantages they offer in construction.

Overview

Purlins are horizontal beams typically made from cold-formed steel sections. Purlins are crucial for supporting the structure of metal roofing systems. They bridge the gap between trusses or joists and effectively distribute loads from the metal panels in a structured way. 

C purlins, with their distinctive curved C-shape, mark an advancement in roll-formed girder technology aimed at improving load distribution performance. 

Offering a bearing capacity range of 700–900 kips per foot, C purlins can efficiently manage the combined weight of roofing materials, snow, and wind uplift essential for industrial buildings that bear heavy loads.

Different Types of Purlins

While C purlins dominate the market, other purlin types cater to specific needs:

• C Purlins: C purlins are shaped like the letter C and are commonly used to provide support for walls and floors. They are designed to serve as the wall and floor joists in a building's structure, making them suitable for supporting the necessary beams for flooring. These purlins are often chosen for cladding due to one plain side, but they also work well for simple span construction.
• Z Purlins: Z purlins have a shape resembling the letter Z and are typically made from cold-formed or rolled sheets. They can save up to 50% on structural sheets compared to hot-rolled angles. Widely utilized in agricultural and industrial structures, Z purlins offer high flexibility and lightweight features that allow them to be adapted for various sizes of constructions.

C purlins account for a significant share of the global purlin market, estimated to be around 65%. This dominance is attributed to their cost-effectiveness, ease of installation, and adequate strength for various roofing applications.

What are C purlins?

C-shaped purlins, as the name suggests, have a shape resembling the letter C and are utilized to fortify the structural integrity of roofing systems. In certain construction projects, C-shaped purlins may serve as support beams in flooring systems; however, for pre-engineered steel building constructions, they are exclusively employed in roofing applications. 

This setup allows the flanges to effectively resist bending pressures, while the web prevents buckling. Attaching them securely to roof panels and trusses at specific intervals enables C purlins to work together with shear connectors in composite action, significantly boosting overall load capacity beyond traditional members. The smooth curve removes vulnerable points where flats meet and enhances durability.

C purlins are available in various sizes and thicknesses; typical depths range from 150 mm to 450 mm. The choice of size depends on factors such as span (the distance between supporting structures), weight of roofing material (heavier materials require sturdier purlins), and local wind and snow loads specified by building codes for a particular region.

What is the Standard Size of C Purlins?

While specific dimensions may vary slightly between manufacturers, the following table provides a general overview of standard C purlin sizes:

Conclusion

In conclusion, C purlins represent the pinnacle of curved steel girder technology for roofs. Their intrinsic ability to efficiently manage heavy loads through composite action with roof panels has transformed the industrial building sector. 

Ongoing advances in roll forming now offer high-strength and even cold-formed options to meet a broader array of design challenges. When correctly specified, installed and maintained, C purlins provide enduring support critical to sheltering commerce and community.